CRGO Steel Transformer Plant
Vijai operates from a chain of facilities based in Hyderabad (South India), Uttarakhand (North India) and an overseas unit in Brazil. The manufacturing units of Vijai represent the best form of manufacturing process that is based on the concept of Vertical Integration or Backward Integration. This helps us to create an effective system that maintains its good hold on Pricing, Delivery and most important aspect above all, QUALITY.
Over a built-up area of around 20000 m² is the manufacturing unit for Vijai for Transformers with CRGO Silicon Steel Core and is capable of manufacturing Transformers till 15 MVA, 66 kV class. The plant has automatic Core cutting and processing line along with annealing furnaces. It also has a dedicated winding bay for both Low Voltage and High Voltage Coils for different capacities.
This plant is capable of rolling out the following products.
- Single Phase DistributionTransformers.
- Small and Medium Range Distribution Transformers
- Completely self protected Transformers.
- Pad Mounted Transformers.
- Dry Type Cast Resin Transformers
- Small Power Transformers(Oil Filled)
- Transformers with Corrugated Tank .
Prime grade CRGO steel core is imported in the form of rolls and then slit into coils of smaller widths. These strips are then cut to length's based on the design parameters for a specific job. These core laminations are then passed through a Continuous Annealing Furnace to remove any stress concentrations that may arise due to the shearing operation.
The annealed cores are now ready for the core forming or stacking operation. Cores are wound or stacked based on the customer prerequisites. The wound cores are sent for annealing in the batch annealing furnace under Nitrogen gas for a complete cycle and then sent forward for core coil assembly process.
Winding is done on semi automatic machines in Vijai wherein the wires for winding are processed in a captive wiring plant. These wires are wound on a bobbin which is then sent to the winding section. Highly experienced and proficient workers then wind these wires over a specific mandrel which has prefixed diameters as per the specification from the engineering department.
Winding can be Spiral, helical or crossover coils based on the specific requirement to achieve the technical parameters. Some of the coils are then tested for continuity and sent for mechanical compression under vacuum to achieve the axial heights as prescribed by the engineering department from whereon they are sent for core coil assembling.
Core Coil Assembling Process
- The core assembly is vertically placed with the foot plate touching the ground. The top yoke of the core is removed.
- The limbs of the core are tightly wrapped with cotton tape and then varnished. Cylinder made out of insulating press board is wrapped on all the three limbs. Low Voltage Coil is placed on the insulated core limbs.
- Insulating block of specified thickness and number are placed both at the top and bottom of the L.V.Coils Cylinder made out of corrugated paper or plain cylinder with oil ducts are provided over L.V.Coils.
- H.V. Coils are placed over the cylinder. Gap between each section of H.V. Coils including top & bottom clearances is maintained with the help of oil ducts, as per the design/drawings. The Top Yoke is refilled. Top core frame including core bolts and tie rods are fixed in position. Primary and secondary windings are connected as per the requirements.
- Phase barrier between H.V. phases are placed as per requirement. Connections to the tapping switch (if required) are made.
- The winding leads are then carefully brought out on the top or side as per the wiring diagram. The tap changers and necessary accessories such as lugs are then attached to the winding leads. On the LV side copper bars are then brazed to the winding leads.
- The CCA is then ratio tested to check the uniformity of the number of turns in the winding.
These core coil assemblies are then sent to the tanking department for further process.
Tanking and Oil filling:
| Tank fabrication (for CRGO and AMT):
Conventional rectangular tanks and circular tank with dome shaped covers are designed to withstand specified vacuum and pressure up to 0.8Kg/cm2. Tank welding is carried out by using automatic / semi-automatic MIG welding machines. Vijai also has a Robotic Welding machine to ensure maximum accuracy and repeatability of the process which yields defect free semi finished tanks for Three Phase Transformers.
To minimize number of welds on the tank body, VEL offers a rounded Rectangular tank which requires only one weld on the side. This ensures the homogeneity of the tanks that result in good mechanical properties as the body of the tank is formed from one single sheet metal.
Resistance to leaks and breathing:
The cover is sealed positively to the tank by a continuous nitrile gasket.
The gasket inhibits breathing or leaking. Welded tanks are tested for leaks after fabrication and tested.
Pretreatment of tank surface:
Pretreatment, such as cleaning and phosphating operations are carried out by seven tank processes before painting to ensure ability to withstand corrosion. Shot blasting is another method which is done under a closed chamber in accordance with Swedish standard SIS 05590.
Shot Blasting enables the surface to become free from visible oil, grease, dirt and rust resulting in effective adhesiveness of paint.
Painting of tank surface:
Tank and cover are coated with high quality powder coating by electrostatic deposition method and then baked at a regulated temperature. Tanks are coated inside with the same polyester powder as the outer side. The advantages of powder coating is as follows.